1. Field of the Embodiments herein
The embodiments of the embodiments herein generally relate to preventing damage to the thermal interface materials that exist between semiconductor chips and lids which are positioned above the chips, and, more particularly, to a structure and method that causes the thermal interface material to have different regions of compression.
2. Description of the Related Art
Integrated circuit structures are commonly formed on wafers which are divided into chips. These chips are usually mounted on substrates and are connected to cooling mechanisms using items such as thermal pastes. One issue that arises with such structures relates to moisture or temperature-induced thermal degradation in the thermal interface material (TIM) that is usually positioned between the chip and the overlying cap or lid. This moisture or temperature thermal degradation prevents reliable low-temperature operation of the electronic package throughout its field life.
For example, such structures can suffer from a moisture induced shape flattening mechanism. The initial die curvature of a chip depends on the laminate, underfill material and its curing conditions. Because of such curvature, the thermal interface material can tear during the curing process. This tearing can occur differently at the center relative to more manageable tears that may occur in the ends (corners and edges) of the thermal interface material. For example, with lower keff (effective thermal conductivity) TIMs, tears can occur at the center of the TIM, while higher keff TIMs usually experienced tears in the corners of the TIM.
Further, temperature and humidity can cause die flattening. Die flattening causes the TIM to stretch, which further decreases keff at center and also causes thermal performance degradation. Other variables which can induce similar issues include laminate warpage, choice of encapsulation cure conditions (cure temperature and stree-free temperature (T-ref) for seal adhesive and Thermal Interface Material) and Lid/laminate surface condition (seal adhesion; gel adhesion and integrity).